A woman has been diagnosed with the measles after travelling to the Philippines bringing the total number of cases in NSW since Christmas to 12.

Another person has been diagnosed with the measles in NSW with the state's health department urging people travelling to Southeast Asia to make sure they are vaccinated.

The woman was likely to have been infected in the Philippines and was briefly hospitalised after developing a rash, NSW Health said in a statement.

She has since been discharged and is recovering.

The woman is the 12th person in NSW to be diagnosed with the measles since Christmas.

She was infectious on flight SQ231 from Singapore to Sydney which arrived at Sydney International Airport about 12pm on January 22.

Passengers on this flight and people in Sydney airport around lunchtime on January 22 are advised to watch for signs and symptoms of measles until February 9.

"If you develop symptoms please call ahead to your GP so you do not wait in the waiting room with other patients," NSW Health's Vicky Sheppeard said.

The department has urged people travelling to Southeast Asia - which is experiencing an outbreak of measles - to ensure they are fully vaccinated before heading overseas.

Measles is highly contagious and is spread in the air through coughing or sneezing.

Symptoms include fever, sore eyes and a cough followed three or four days later by a red, blotchy rash spreading from the head and neck to the rest of the body.